1 CP per 1" works pretty well, just keep in mind the Speed Examples table from 7.2. Even the most powerful jetpack isn't going to make you go faster than a fighter plane (20"), for instance, and even that speed would be pretty ridiculous.

My instinct is to say that a minifig can run and turn and hop around all he wants for his normal movement inches, but all the jetpack inches have to be in a straight line, just like Sprinting.

Let's also not rule out jump jets. Very useful for quickly gaining access to higher vantage points either for offensive purposes or getting the hell out of bad situations. When a minifig is equipped with a jump jet, he can move his normal lateral movement amount in a straight line, but also upwards (and back down) up to 6 inches.